In-hub spindle motor with separate fluid dynamic bearings

ABSTRACT

A hydrodynamic bearing system where the bearing includes a shaft and two independent bearings, including a top cone or bi-sphere and a bottom cone or bi-sphere separated by a segment of the shaft. The bearing includes a hub supported bearing element rotating around the shaft and the shaft supported top cone and bottom cone; complementary surfaces of the bearing element and the cone define a narrow gap between the bearing support element for the bearing fluid. Sealing plates or seal elements define a fluid gap with a radially extending face of the cone; a gap also exists between an interior surface portion of each cone and the shaft. These gaps are connected so that separate flow paths are established, one around the top cone or bi-sphere and one around the bottom cone or bi-sphere. By providing two independent bearings, the stator can be mounted to the shaft, facing magnets supported on the hub to form an in-hub motor. When the load or RPM changes, the fluid pressure or movement in each bearing may change but the function of the bearing and its ability to provide stiffness and stability to the system will not be lessened.

CROSS-REFERENCE TO RELATED APPLICATION

This continuation application claims priority to U.S. application Ser.No. 09/060,225 filed Apr. 14, 1998, now U.S. Pat. No. 6,118,620.

This invention is based on U.S. Provisional Patent Application, SerialNo. 60/064,501, filed Nov. 5, 1997, assigned to the assignee of thisapplication and incorporated herein by reference. This application is acontinuation-in-part of U.S. application Ser. No. 08/994,099, filed Dec.19, 1997, now U.S. Pat. No. 6,144,523, entitled “SIMPLIFIED CONICALBEARING WITH INDEPENDENT FLOW PATHS” by Murthy, et al., assigned to theassignee of this application and incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to disc drive storage systems, and morespecifically, the present invention relates to a hydrodynamic fluidbearing for use in a disc drive storage system.

BACKGROUND OF THE INVENTION

Magnetic disc drives are used for magnetically storing information. In amagnetic disc drive, a magnetic disc rotates at high speed and atransducing head “flies” over a surface of the disc. This transducinghead records information on the disc surface by impressing a magneticfield on the disc. Information is read back using the head by detectingmagnetization of the disc surface. The transducing head is movedradially across the surface of the disc so that different data trackscan be read back.

Over the years, storage density has tended to increase and the size ofthe storage system has tended to decrease. This trend has lead togreater precision and lower tolerance in the manufacturing and operatingof magnetic storage discs. For example, to achieve increased storagedensities the transducing head must be placed increasingly close to thesurface of the storage disc. This proximity requires that the discrotate substantially in a single plane. A slight wobble or run-out indisc rotation can cause the surface of the disc to contact thetransducing head. This is known as a “crash” and can damage thetransducing head and surface of the storage disc resulting in loss ofdata.

From the foregoing discussion, it can be seen that the bearing assemblywhich supports the storage disc is of critical importance. One typicalbearing assembly comprises ball bearings supported between a pair ofraces which allow a hub of a storage disc to rotate relative to a fixedmember. However, ball bearing assemblies have many mechanical problemssuch as wear, run-out and manufacturing difficulties. Moreover,resistance to operating shock and vibration is poor, because of lowdamping. Thus, there has been a search for alternative bearingassemblies for use with high density magnetic storage discs.

One alternative bearing design which has been investigated is ahydrodynamic bearing. In a hydrodynamic bearing, a lubricating fluidsuch as gas or a liquid provides a bearing surface between a fixedmember of the housing and a rotating member of the disc hub. Typicallubricants include oil or ferromagnetic fluids. Hydrodynamic bearingsspread the bearing interface over a large continuous surface area incomparison with a ball bearing assembly, which comprises a series ofpoint interfaces. This is desirable because the increased bearingsurface reduces wobble or run-out between the rotating and fixedmembers. Further, improved shock resistance and ruggedness is achievedwith a hydrodynamic bearing. Also, the use of fluid in the interfacearea imparts damping effects to the bearing which helps to reducenon-repeat runout.

However, some hydrodynamic bearing designs themselves suffer fromdisadvantages, including a low stiffness-to-power ratio and increasedsensitivity of the bearing to external loads or shock.

A desirable solution to this problem would be to have the spindle motorattached to both the base and the top cover of the disc drive housing.This would increase overall drive performance. A motor attached at bothends is significantly stiffer than one held by only one end.

Typically, hydrodynamic motor designs provide no method for top coverattachment. The reason for this is that in order to have top coverattachment, the motor (i.e. the fluid bearing which separates the fixedand moving parts) would need to be opened on both ends. Opening a motorat both ends greatly increases the risk of oil leakage out of thehydrodynamic bearing. This leakage among other things is caused by smalldifferences in net flow rate created by differing pumping pressures inthe bearing. If all of the flows and pressures within the bearing arenot carefully balanced, a net pressure rise toward one or both ends mayforce fluid out through the capillary seal. Balancing the flow rates andpressures in conventional, known fluid bearing designs is difficultbecause the flow rates created by the pumping grooves are a function ofthe gaps defined in the hydrodynamic bearing, and the gaps, in turn, area function of parts tolerances. Thus, a need exists for a new approachto the design of a hydrodynamic bearing based motor to optimize dynamicmotor performance stiffness, and damping.

It is also desirable to design a hydrodynamic bearing which is open atboth ends for other purposes than fixing both ends of the shaft to thebase and cover of a housing. For example, with such an open-endeddesign, either end (or both) could be extended beyond the sleeve to becoupled to a driver or load, or for other purposes.

An effort has been made to address some of these problems with a conicalbearing having independent flow paths. This design is disclosed in U.S.application Ser. No. 09/043,066, filed Dec. 19, 1997, now abandoned,entitled “CONICAL HYDRODYNAMIC BEARING WITH TWO INDEPENDENT CIRCULATIONPATHS”, by Jennings, et al., assigned to the assignee of thisapplication and incorporated herein by reference. However, furtherconsideration indicated that it would be desirable to simplify the twoindependent flow paths. Further, it is also desirable to make thecapillary seals at the ends of the shaft as reliable as possible. It isalso desirable to make the design of the shaft as simple as possible inorder to reduce manufacturing costs and maintain achievable tolerances.It is especially attractive to make the shaft and any element itsupports narrow, but stable, so that an in-hub design can be achieved.

SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to create an improvedhydrodynamic bearing which is relatively insensitive to changes in loadand rotational speed.

Yet another objective of the present invention is to provide ahydrodynamic bearing motor in which the bearing is open at both theupper and lower ends.

A related objective of the invention is to provide a hydrodynamicbearing open at both ends in which the balance of fluid flow or pressurewithin the total system is maintained.

A further objective of the invention is to design a hydrodynamic bearinguseful in a spindle motor or the like in which the motor could beattached to both the top cover and the base of the housing for thespindle motor.

Another objective of the invention is to provide a hydrodynamic bearinguseful in a spindle motor or the like which is stiffer than knownstandard spindle motors which are supported only at one end.

Another objective is to provide a hydrodynamic bearing design havingbalanced internal fluid pressures during operation to minimize thelikelihood of any lubricating fluid being lost during operation.

These and other objectives of the present invention are achieved byproviding a hydrodynamic bearing useful as a bearing cartridge or as thecartridge may be incorporated into a spindle motor or the like, wherethe bearing includes a shaft and two independent bearings, comprising atop cone or bi-sphere and a bottom cone or bi-sphere separated by asegment of the shaft. More specifically, the bearing includes a hubsupported bearing element rotating around the shaft and the shaftsupported top cone and bottom cone; complementary surfaces of saidbearing element and said cone define a narrow gap between the bearingsupport element for the bearing fluid. Sealing plates or seal elementsdefine a fluid gap with a radially extending face of the cone; a gapalso exists between an interior surface portion of each cone and theshaft. These gaps are connected so that separate flow paths areestablished, one around the top cone or bi-sphere and one around thebottom cone or bi-sphere. By providing two independent bearings, thestator can be mounted to the shaft, facing magnets supported on the hubto form an in-hub motor. When the load or RPM changes, the fluidpressure or movement in each bearing may change but the function of thebearing and its ability to provide stiffness and stability to the systemwill not be lessened.

In one embodiment, a grooved pumping seal is provided surrounding theshaft pumping against the pressure established by the bearings at eachend of the shaft, so that the system is well lubricated but does notlose fluid.

The bearing and bearing cartridge embodiments are also characterized byease of assembly of the conical bearing spaced from each other along theshaft.

The hydrodynamic bearing assembly, and bearing cartridge, as disclosedherein used in a spindle motor, provides enhanced stiffness and dampingwithin the cartridge system.

At each end of the shaft, a capillary seal is defined to prevent leakageof the bearing fluid into the outer atmosphere. In at least oneembodiment, a unique centrifugal capillary seal is utilized to preventfluid loss; this seal is designed to pump fluid from the outer end ofthe gap toward the conical bearing gap when the hub is rotating.

According to certain preferred embodiments, the hub supporting elementadjacent each conical bearing seals are provided to extend from theouter region of the conical seal radially across the space defined forthe stator and supporting the magnet and back iron and hub. Thus, thespace inside the hub is sealed, enabling a simplified filling sequencefor the hydrodynamic bearing based on pressure differential.

Other features and advantages of the present invention would becomeapparent to a person of skill in the art who studies the presentinvention disclosure given with respect to the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a disc drive in which thepresent invention is useful.

FIGS. 2 and 3 are vertical sectional views of prior art hydrodynamicbearing designs.

FIG. 4 is a vertical sectional view of a first embodiment of thisinvention.

FIG. 5A is a vertical section of a second embodiment of the invention.

FIG. 5B is a vertical section of one hydrodynamic bearing, together withthe adjacent sealing means.

FIG. 5C is a perspective view of the bearing cone which is shaft mountedto form the hydrodynamic bearing.

FIG. 5D is an exploded view of the motor embodiment also shown in FIG.5A.

FIG. 6A is a vertical sectional view of an alternative, third embodimentof the invention; FIG. 6B is an enlarged view of a detail of theembodiment, including an alternative sealing means for the interior ofthe motor.

FIG. 7 is a vertical sectional view of an alternative embodimentutilizing a rotating shaft supported by the bearing and sealing means ofthe invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is an exploded perspective view of a magnetic disc drive storagesystem in which the present hydrodynamic bearing cartridge could beused. In the example to be discussed below, the use of the hydrodynamicbearing and associated cartridge will be shown in conjunction with aspindle motor. Clearly, this bearing design is not limited to use withthis particular design of a disc drive, which is shown only for purposesof the example. The bearing cartridge (that is the bearing and motorelements, excluding the hub which is attached to support a disc) alsohas numerous other uses outside the field of disc drives.

In this particular example, the storage system 10 includes a housingbase 12 having spindle motor 14 which rotatably carries storage discs16. An armature assembly 18 moves transducers 20 across the surface ofthe discs 16. The environment of discs 16 is sealed by seal 22 and cover24. In operation, discs 16 rotate at high speed while transducers 20 arepositioned at any one of a radially differentiated track on the surfaceof the discs 16. This allows the transducers 20 to read and writemagnetically encoded information on the surfaces of discs 16 at selectedlocations. The discs rotate at very high speeds, several thousand RPM,in order to maintain each transducer flying over the surface of theassociated disc. In present day technology, the spacing distance betweenthe transducer and the rotating disc surface is measured in microinches;thus it is absolutely essential that the disc does not tilt or wobble.

FIG. 2 is a cross sectional view of a further prior art drive spindleassembly of a type which can be supported only from the base of thehousing of the system using the hydrodynamic bearing cartridge, in thiscase a disc drive assembly. The figure is taken from U.S. Pat. No.5,559,651, which is assigned to the assignee of the present applicationand is incorporated herein by reference.

In FIG. 2, the cartridge 40 which includes the hydrodynamic bearing isshown incorporated in a spindle motor 50 which is usable to drive thediscs in the disc drive 10 of FIG. 1. The design includes a drive rotoror hub 14 rotatably coupled to the shaft 52. The shaft 52 includes anupper hemisphere or convex portion 54 and a lower hemisphere or convexportion 56 received in sleeve 58 which rotates relative to the shaft.The shaft 52 is fixedly attached to the base 60, which may beincorporated in or supported from the housing base 12 described withrespect to FIG. 1. The sleeve 58 receives the journal 62 of shaft 52 andhas upper hemisphere shaped, concave receptacle 64 and lower hemisphereshaped concave receptacle 66. A fill hole 68 is also provided to areservoir 59 in (as drawn, the lower end) fixed member 52 to providebearing fluid to the hydrodynamic bearing, and rotor 14 includes acounterplate 70 which is used to close off one end of the hydrodynamicbearing to the atmosphere. In operation, the bearings shown in thisfigure comprises hydrodynamic bearings in which a lubricating fluid suchas oil circulates through gaps between the fixed member which is theshaft and the rotating member which in this case is the sleeve. Rotationof the rotating member causes the lubricating fluid to circulate.

As further shown in FIG. 2, oil is trapped in the hydrodynamic bearingby a diverging capillary seal 72. However, as can also be seen from aninspection of this Figure, this design is not adaptable to being openedto the atmosphere at both ends, as the counterplate 70 is provided atone end to close off the hydrodynamic bearing to the atmosphere, thecounterplate 70 rotating with the sleeve.

FIG. 3 is a variation of the design shown in FIG. 2. This Figure, alsotaken from the '651 patent, illustrates the use of a central reservoir86. Spindle 60 includes a rotor hub 71 which carries disc 73 and isrotatably coupled to shaft 75. Shaft 75 includes upper hemisphere 68 andlower hemisphere 70 received in cartridge sleeve 72. Sleeve 72 receivesjournal 74 of shaft 75. The top portion of shaft 75 is sealed with sealplate 76, and journal 74 extends therethrough. Hub spacer 78 is coupledto rotor hub 71, and carries permanent magnets 80. Shaft 75 is receivedin base 82, and includes fill hole 84. Fill hole 84 connects topassageway or reservoir 86, which extends through the center of shaft75. Passageway 86 connects to center passageway or bore 88 and distalbores 90. In operation, oil flows into bore 86 through center bore 88and out distal bores 90. This is indicated by arrows shown in bore 86.Again, in this embodiment, the fluid circulation paths in thehydrodynamic bearing are sealed off from the outer atmosphere by sealthrust plate 76.

The present invention will next be described with respect to thefollowing figures. This application will disclose in detail the overallmotor design. Details of several of the structural elements which appearherein can also be found by referring to the cited co-pending patentapplication which are incorporated herein by reference.

Overall, the design for the present in-hub spindle motor resulted fromthe need to incorporate fluid dynamic bearings (FDB) in a spindle motor,utilizing an in-hub configuration, without compromising theelectromagnetic efficiency of the motor. By splitting the bearings intotwo mirror images which are at or close to opposite ends of the shaft,little or no more bearing space is utilized than in a ball bearingmotor, allowing the achievement of a in-hub design with a relativelysmall cross-section.

More conventional FDB motors (other than shown in FIGS. 2 and 3) utilizea journal bearing and a thrust plate to react radially and axiallyforces. The journal bearing utilizes a significant amount of volumealong the central portion of the shaft of the motor, detracting from thespace available for electromagnetics, and compromising the size of thein-hub configuration desired. By utilizing separate FDB's, at each endof the shaft as disclosed herein, which in a preferred embodiment aremirror images of each other although modifications of one may beutilized for various operational or design efficiencies, then no morespace is used than the ball bearings that these FDB's replace. The motoris built-up from the stator-shaft assembly outward. The motor bearingsare filled with oil either with pressure activated seals (which may beeasily incorporated into the present design) or through capillaryattraction.

The sealing itself at the ends of the shaft, both of which are opened sothat both ends of the shaft may be fixed, is accomplished either with apair of centrifugal capillary seals and groove pumping seals, or withone of a centrifugal or capillary seal at the other end of each cone.The present design also lends itself easily to stator interconnectionwires being routed through the center of the shaft, and attached to anintegral connector at the bottom of the shaft.

Referring to FIG. 4, the figure shows an exemplary in-hub spindle motorwith a split fluid dynamic bearing arrangement with two totally separatefluid dynamic bearings 102, 104 mounted at or near opposite ends of ashaft 106 and on opposite sides of a stator 108 mounted on the externalsurface of the central section of the shaft 110 intermediate to fluiddynamic bearings. Preferably, the fluid dynamic bearings 102, 104 aremirror images of each other. Each comprises (referring to one of thebearings), a bearing cone 112 which is preferably press fit on anexternal surface of the end section of the shaft 106 and a bearing seat114 having a section 116 which is mounted to or press fit on a sectionof the shaft between the bearing cone 112 and the central section 110 ofthe shaft. The bearing cone 112 and seat 114 include complementarysurfaces 116, 117, respectively, which together define a portion of thefluid dynamic bearing gaps. As the upper and lower bearing seats 114,115 which support the back iron 120, magnet 122 and hub 124 rotateoutside the shaft 106 and the stator 108 of the motor, fluid ismaintained in the gap 126 between the bearing cone 112 and the seat 114to establish a bearing means for allowing this free rotation. The fluidis intended to circulate and be maintained in gaps defined around allthree sides of the cone 102, 104. Therefore, each bearing seat 114, 115supports at its axially distal end from the center of the shaft acounter-plate 128, 129, respectively, which is spaced from a surface ofthe bearing cone 102, 104 to establish a fluid gap 130, 131. The bearinggap is completed through openings 132, 133 between the radially innersurface of each cone 102, 104 and the surface of the shaft 106. Theseopenings 132, 133 may be formed on either the outside of the shaft orthe inside of the cone. Thus a complete fluid path is established aroundall three sides of each bearing cone.

One of the complementary surfaces 116, 117 of each bearing cone andcomplementary bearing seat has grooves so that proper fluid pressuresare established and circulation is established and maintained throughthe entire circulation path described so that the bearing seats 114,115, magnet 122, back iron 120 and hub 124 all rotate freely around theshaft with energization of the stator 108. To prevent fluid fromescaping from the fluid dynamic bearing either into the interior regionof the motor, or to the atmosphere surrounding the motor, capillaryseals are provided on either side of each fluid dynamic bearing.Referring, for example, to the fluid dynamic bearing 102, a capillaryseal 135 is established between relatively diverging walls of the shaft106 and seat 115; similarly, a capillary seal 136 is established at theopposite end of the FDB by providing relatively diverging walls betweenthe shaft 106 and the thrust plate 129. This diverging wall capillaryseal construction is well known in this technology and need not beexplained further.

A means for leading the control wires to the stator 108 from an externalpower source is provided comprising a slot 140 in the central section ofthe shaft 110 connecting the stator 108 to a connector which may beprovided in the hollow or partially open central section of the shaft106. Further details of this connection may be found by reference to anapplication of Grantz, et al. entitled, “LOW PROFILE IN-SHAFTCONNECTOR,” U.S. application Ser. No. 09/059,888, filed Apr. 14, 1998,now U.S. Pat. No. 5,997,357, filed contemporaneously herewith andincorporated herein by reference.

It can further be seen that this design by providing bearing seats 114,115 aligned above and below the stator, and supporting opposite ends ofthe back iron and hub, establishes a sealed interior 142 for the stator.Sealing the interior of the in-hub motor diminishes the possibility ofgenerating particles or other contamination which can escape to theatmosphere surrounding the motor. The design also provides for andfacilitates filling the fluid dynamic bearings with bearing fluid byproviding a pressure activated seal 144. This seal could be a formedseal or an O-ring which would normally be in retracted state, allowingfree rotation of each bearing seat relative to the shaft 106. Whenactivated, by creating a pressure differential between the atmospheresurrounding the motor and the internal region 142 of the motor which isnow possible because of the sealed nature of the internal region 142,this seal 144 would expand and fill the space between each bearing seat114, 115 and the region of the shaft 106 where the seat is mounted.Fluid could now be drawn into the internal region of each fluid dynamicbearing 102, 104 but could not escape into the internal region of themotor 142 past this pressure activated seal. Seal 144, as is well knownin this field, would retract when the pressure differential is removed,allowing again the free rotation of the bearing seats relative to theshaft. The fluid would now be restrained within each fluid dynamicbearing by the presence of the capillary seals.

It should be noted that, although the figures show that the surfaces ofthe FDB's 102, 104 are spherical, this design and the other designs tobe disclosed in this application work equally well with mating conicalsurfaces or surfaces of other advantageously designed profiles such astaught in the application “Conical Bearing With Lenticular Profile,”invented by Leuthold, et al., U.S. application Ser. No. 09/060,312,filed Apr. 14, 1998, now U.S. Pat. No. 6,019,516, filedcontemporaneously herewith and incorporated herein by reference.

An alternative and preferential embodiment is shown in FIG. 5A; theprimary elements of the assembled design of FIG. 5A appear in explodedform FIGS. 5C and 5D. FIG. 5B will be referred to to illustrate andexplained the means for establishing pressure differentials which areutilized to maintain and enforce the fluid distribution over thesurfaces of the conical bearings, as well as means for expelling any airbubbles which may intrude into the fluid bearing surface.

As with the design of FIG. 4, a fixed shaft 500 supports grooves,spherical or conical bearings 102, 104 and is supported near theopposite ends of the shaft. The central section 508 of the shaftdirectly supports a stator 510 which cooperates with a magnet 512. Thestator mounting, with its inner dimension generally aligned between theFDBs, provides a narrow profile for this in-hub motor. The magnet 512 issupported from a back iron 514 on the interior surface of hub 516 sothat energization of the stator 510 causes rotation of the hub and thedisc or discs 518 supported thereon. It can be seen that the bearingseats 506, 508 extend radially from the shaft out beyond the radialdimension of the shaft supported stator 510 and support the back iron514 and the hub 516. This defines an enclosed space 520 for the statorand magnet, enclosing a possible source of contaminants. A pressureequalizing filter 522 is incorporated into at least one of the bearingseats 506. The filter extends at least part way through an opening 523which extends entirely through the bearing seat 506 so that nocontaminants generated within space 520 can escape. Defining thisenclosed space also allows implementation of the vacuum fillingtechnique described with respect to FIG. 4 even in this embodiment; theopening 523 itself could simply be plugged while filling occurs. Thestator itself is connected to the necessary control wires to energizethe stator through a multi-pin plug connector 527, whose wires extendthrough a slot 524 in a wall of the shaft 500 to be connected to thestator windings 510. Details of this connector can be found in U.S.application Ser. No. 09/059,888, filed Apr. 14, 1998, now U.S. Pat. No.5,997,357, entitled “LOW PROFILE IN-SHAFT CONNECTOR,” Grantz, et al.,filed contemporaneously herewith and incorporated herein by reference.Therefore, further details of this connector and its insertion into theshaft and connection to the external control wires will not be disclosedherein.

As with the previous embodiment of an in-hub spindle motor, this motoralso is open at both ends, presenting the problem of easily filling thefluid dynamic bearings 502, 504 with bearing fluid, and thereafterpreventing the escape of any such fluid. This invention also addressesthe problem which is posed by the fact that air can sometimes becomeentrapped in the fluid, reducing the effectiveness of the fluid dynamicbearing. Therefore, the present invention incorporates means forexpelling the air from the fluid dynamic bearing, so that theeffectiveness and life time of the bearings are optimized. As with theprevious embodiment, the motor of FIG. 5A incorporates two totallyseparate fluid dynamic bearings on either side of a stator, with nofluid flow along the central section 508 of the shaft, the FDB's beingmounted on either side of this central section. Details of each of thebearings and the general theory of their operation will next be examinedwith respect to FIG. 5B. Further details and alternative approaches tothese designs, which may be incorporated in the present motor, can befound in the following applications all of which are filedcontemporaneously herewith and incorporated herein by reference:

U.S. application Ser. No. 09/060,342, filed Apr. 14, 1998, now U.S. Pat.No. 6,144,161, entitled “GROOVE PUMPING SEAL,” by Grantz, et al.;

U.S. application Ser. No. 09/060,328 filed Apr. 14, 1998, now U.S. Pat.No. 6,154,339, entitled “CENTRIFUGAL CAPILLARY SEAL,” by Grantz, et al.;and

U.S. application Ser. No. 09/060,224, filed Apr. 14, 1998, now U.S. Pat.No. 5,980,113, entitled “ASYMMETRIC SEALING MEANS,” by Grantz, et al.;all of which are assigned to the assignee of the present invention andincorporated herein by reference.

Thus, referring next to FIG. 5B, the sealing design shown in FIG. 5Bresults from the need to providing a very positive sealing means forfluid dynamic bearing motors such as shown in FIGS. 4 and 5A which havetwo independent fluid dynamic bearings. Of course, the design of FIG. 5Band its alternatives could be used with other motors wherever twoindependent fluid dynamic bearings are used. The significance of thedesign, among others, is that it does not require a close balance ofpressure between the top and bottom of the bearing. Further, bycombining the characteristics of the centrifigal capillary sealgenerally indicated at 600 (which provides a means for pushing fluidtoward the fluid bearing when the motor is spinning and for holding thefluid in the gap when the motor is at rest), and the grooved pumpingseal generally indicated at 602 (which provides a means for holding andsealing the fluid in the FDB), together with the conical/sphericalbearing generally indicated at 604, the fluid is positively maintainedon the surface of the bearing. The seals also provide means forexpelling any air bubbles which may enter the bearing system.

As is already well known, the primary support system in the bearingcomprises the bearing cone 608 and the surrounding bearing seat 610.These pieces define facing surfaces 612, 614 which are separated by gap616 of about five microns (although this dimension is representative ofexample only; it may be greater or less depending on the tolerancesachieved by parts and assembly methods). Fluid fills this gap 616, andis maintained under pressure within this gap by grooves 618 on thesurface of the shaft cone 608 which is shown in FIG. 5C. To allow forfluid circulation, and maintenance of the fluid in the gap 616, the gapis extended over the back surface 620 of the bearing cone 608 byproviding grooves running linerally along the back surface of the coneor the facing surface 624 of the shaft. These grooves 622 allow thefluid to pass axially toward the distal end 626 of the shaft 500. Thepath or bearing gap for the fluid is completed through a gap between awall 627, the sealing cone 628 and the upper surface 630 of the bearingcone 608. Most efficiently, the path is through grooves 632 formed inthe top surface 630 of the cone 608 (see the cone detail in FIG. 5C),although the grooves could also be provided in the complementary surfaceof the sealing cone 628.

As is shown by the arrows marked Δp on FIG. 5B, the pumping action ofthe grooves 618 on the face of the cone create a pressure differentialfrom the apex 640 of the bearing cone toward the narrower end 642 of thecone. Thus, the fluid flow over the surface of the cone being generallyfrom the point of lower to higher pressure, is as marked by the arrow644 and continues axially toward the distal end 626 of the shaftfollowing the path marked by arrow 646 and returns to the apex of thecone through the grooves 632 following the pressure arrow 648.

In order to provide a means for fluid to be inserted into the fluiddynamic bearing, as well as to provide a means for air bubbles to beexpelled from the bearing 610, a centrifugal capillary seal 660 isincorporated into the design, leading from the open end 662 of the fixedshaft 500 and relatively rotating parts, down to the apex 640. The sealis formed between a wall 666 of the shield seal 668 which rotates withand is supported from (or even integrated with) bearing seat 506 and hub516, and wall 663 of seal cone 628 which is supported from the shaft.The diverging walls 661, 663 are separated by a measurable gap 662 atthe axially outer end of the seal; the narrowest point is at or near theapex 640 of the sealed design. As disclosed in greater detail in theincorporated applications, the centrifugal capillary seal 660 utilizescentrifugal force which is created by the relative rotation of the walls661, 663 to create a pressure gradient represented by the arrow Δp, 670,to push oil back into the motor whenever the motor is spinning.

Establishing this combination of pressure gradients also provides ameans for expelling air bubbles from the entire fluid dynamic bearingsystem. That is, some air bubbles may appear in the system and have anegative effect on performance. However, by establishing the pressuregradients represented by the various arrows Δp over the surfaces of thebearing cone, and through the capillary seal, the air bubbles can beexpelled. Specifically, it is known that when the pressures areestablished, and the relative rotation has been established, the airbubbles will move from the point of highest pressure to lowest pressure.Therefore, any air bubbles appearing in or near the quiet zone 669 ofthe groove pumping seal 602 (to be explained below) or near the arrowportion 642 of the bearing cone, or along any surface of the bearingcone will move toward the point of lowest pressure which is the apex ofthe bearing cone 608 and sealing cone 628. Once reaching that point, theair bubbles will continue to the point of lowest pressure, moving outthrough the centrifugal capillary seal and being expelled through thecapillary seal. Thus, this system operates to continuously purge itselfof any air which might inadvertently enter the system, while veryeffectively sealing the fluid within the bearing system.

In order to further enhance the sealing stiffness of the system, agrooved pumping seal 602 is provided, typically and preferablyimmediately axially inward from base 642 of the bearing cone, betweenthe bearing cone and the central portion of the shaft where the statoris mounted. This grooved pumping seal 602, in a preferred form, can bedefined on the face of a central section 660 of the bearing seat 608which also supports one of the two faces of the fluid dynamic bearing.In a preferred form, this grooved pumping seal comprises an ungroovedsurface section or quiet zone 662 surrounding a portion of the ungroovedshaft immediately adjacent the base 642 of the bearing cone, and agrooved pumping region 664 which also closely surrounds an ungroovedsection of the shaft immediately adjacent the quite zone 662. Thisgrooved pumping seal 602 is intended to be a low volume, very highstiffness seal. It is a capillary seal which employs active pumping byvirtue of the presence of relatively deep grooves in one section 664 ofthe seal to provide very high sealing stiffness. When the shaft is atrest, the oil settles into the grooves but cannot pass further down theshaft because of the capillary effect of the grooves and diverging ends.When the motor spins up, the relative rotation of the shaft 500 and thesurrounding section 664 of the grooved pumping seal create the pressuregradient indicated by the arrow Δp, 666. This causes an oil fluid flowout of the grooves into the quiet zone 660 as indicated by the arrow668. Further, because of this quiet zone, there is no pumping action toforce the oil out of the grooved pumping seal into the fluid dynamicbearing, so that the necessary fluid for effective operation of thisgrooved pumping seal is maintained. Finally, as explained above, any airbubbles which appear in the quiet zone would tend to move contrary tothe pressure gradients in the fluid dynamic bearing and be expelled fromthe distal end of the shaft through the centrifugal capillary seal; anyfurther air bubbles which moved into the grooves of the groove section664 could be expelled into the interior section of the motor because ofthe strong pressure gradient created by the rotation of the groovedpumping seal.

Finally, it should be noted that the depth of the grooves and/or thewidth of the grooves diminishes as the oil is moved up through thegrooved pumping zones 664 into the quiet zone 660. This enhances andprovides a means for pumping the oil efficiently out of the grooves intothe quiet zone during motor operation, while providing a strongcapillary effect in the grooves to maintain the oil in the groovedpumping seal 602 when the motor is not in operation.

It should be further noted that although the preferred embodiment ofthis design discloses utilizing grooves on the central section of thebearing seat, a separate grooved piece could be provided separate andapart from the bearing seat; and in a further alternative, that thecentral section of the bearing seat which surrounds the shaft could beleft entirely smooth, and the grooves instead imposed upon the shaft,although this would presumably create some further fabricationdifficulties.

FIG. 5D shows the relative position and scale of the individual elementswhich make up the exemplary motor of FIG. 5A; a further explanation ofthe individual elements and the manner in which they are assembled intoa completed motor can be found in U.S. application Ser. No. 09/060,030,filed Apr. 14, 1998, now U.S. Pat. No. 6,148,501, entitled “FABRICATIONMEANS FOR IN-HUB SPINDLE MOTOR WITH SEPARATE FLUID DYNAMIC BEARINGS,” byGrantz, et al., filed contemporaneously herewith and incorporated hereinby reference.

It may further be noted that the bearing seats 608 also includes agroove 680 in the upper surface thereof. A flexible gasket 682 iscaptured in this groove 680 between the surface of the bearing seat andan arm of the shield seal. As the pressures and fluid flow at the apex640 according to this design can be noticeable, this gasket provides ameans for preventing the radial escape of any fluid away from the fluiddynamic bearing and the centrifugal capillary seal.

A further exemplary alternative to the present invention is illustratedin FIGS. 6A and 6B. It can be seen that this embodiment alsoincorporates a pair of symmetrical fluid dynamic bearings 700, 702isolated at the open ends of the shaft by capillary seals 704, 706. Ascan be seen, the lower of the two bearings is also isolated from theinterior 708 of the motor by further capillary seal 710. The upper fluiddynamic bearing 700 is isolated by a rotary contact seal 712. Thisrotary contact seal, shown in greater detail in FIG. 6B, includes a maleportion supported on a shelf 716 of the shaft and a female overlappingportion 718 supported on the bearing seat 720. The use of this type sealenhances the sealing effect at the base of one or both of the two fluiddynamic bearings, to facilitate assembly of the overall motor whilediminishing the possibility of fluid escape into the center of themotor.

This is especially useful where a vacuum filling technique is to be usedto draw fluid into the motor. Such techniques are well known in thisfield. The change in pressure activates the seals 714, 718 to seal thebearings from the interior of the motor. Then fluid provided adjacentthe distal end of the shaft is drawn into the bearing by the pressuredifferential.

FIG. 7 illustrates the application of the principles of the invention toa rotating shaft design. The Figure shows a motor with rotating shaft700 supporting a magnet 702 on a central section. The magnet 702cooperates with stator 704 to cause rotation of the shaft. The hub, ofcourse, is supported in place by supporting means (not shown) attachedto the bearing seats 706, 708 which support the hub 710. Thehydrodynamic bearing is otherwise as explained with respect to thepreceding Figure showing fixed shaft designs.

Other alternatives to the present design disclosed herein may be withinthe skill of the art and apparent to a person who studies thisdisclosure. For example, grooved pumping seals could be used on eitherside of each fluid dynamic bearing; similarly, centrifugal capillaryseals could be used above and below each fluid dynamic bearing. Further,in the hydrodynamic bearing and the grooved pumping seal, the groovesmay be impressed on either surface without departing from the spirit ofthe invention. Therefore, the scope of the present invention is to belimited only by the following claims.

What is claimed is:
 1. A spindle motor for use in a magnetic datastorage system including a rotating shaft having a central section andtwo independent fluid dynamic bearings on opposite sides of said centralsection, each of said bearings comprising a bearing cone fixed to theshaft and tapering radially inwardly towards said central section, and abearing seat fixed around the shaft, each of the bearing seats having afluid bearing surface facing a surface of said bearing cone across afirst gap to thereby establish a first section of a fluid dynamicbearing, each of said fluid dynamic bearings further comprising anopening defined between an inner surface of said bearing cone and asurface of said shaft, and a second section of a gap defined between aradially extending surface of said bearing cone and a surface fixed tosaid bearing seat, so that a continuous gap is formed around each ofsaid bearing cones, and a fluid in said continuous gap separating saidfacing surfaces of said bearing seat and said bearing cone to allow freerotation of said shaft and said bearing cone, and a centrifugalcapillary seal on one side of each said bearing cone and a groovedpumping seal on an opposite side of each said bearing cone to isolateand contain said fluid within said independent fluid dynamic bearings.2. The spindle motor as claimed in claim 1 wherein said bearing seatsextend radially and angularly away from said shaft, and support a hubextending axially between said bearing seats to define an enclosedregion around said shaft.
 3. The spindle motor as claimed in claim 2further incorporating a magnet supported on said central section of saidshaft and aligned with a stator supported from said hub so thatenergization of said stator causes rotation of said shaft.
 4. Thespindle motor as claimed in claim 3 wherein said magnet is generallyaligned with said bearing cones of each of said fluid dynamic bearingsso that an in-hub motor of narrow cross-sectional dimension is defined.5. A fluid dynamic bearing system as claimed in claim 4 wherein saidbearing cone surfaces are substantially spherical in cross-section. 6.The spindle motor as claimed in claim 4 wherein each said bearing seatextends around said bearing cone and includes an annular sectionsurrounding the shaft and defines the grooved pumping seal with saidshaft.
 7. The spindle motor as claimed in claim 6 further including apressure activated bearing seal between said bearing cone and saidcentral section of said shaft, said bearing seal being activated by achange in pressure in an interior space of said motor defined by saidbearing seat and said hub extending between said bearing seats,activation of said pressure activated seal allowing filling of saidfluid dynamic bearing with said fluid.
 8. A fluid dynamic bearing systemas claimed in claim 1 wherein bearing cone surface and said bearing seatsurface are complementary.
 9. The spindle motor as claimed in claim 8wherein said bearing cone has a generally bi-spherical bearing surface,and said bearing seat has a spherical surface to define said firstsection of said continuous gap.
 10. The spindle motor as claimed inclaim 8 wherein a magnet supported from the shaft is generally alignedwith said bearing cones of each of said fluid dynamic bearings so thatan in-hub motor of narrow cross-sectional dimension is defined.
 11. Amagnetic disc storage system comprising: a base, a rotatable magneticstorage disc having an axis of rotation, a transducing head for readingand writing information on the disc, a rotating shaft supported in saidbase having a central section supporting a magnet, and independent fluiddynamic bearings on opposite sides of said central section of said shaftlocated near to said base and distant from said base on the oppositeside of said magnet, said fluid dynamic bearings each comprising agenerally conical bearing member supported from said shaft and having agenerally conical surface extending inwardly toward said central sectionof said shaft and cooperating with a facing generally conical surface ofa bearing seat, said bearing seats extending generally radially awayfrom said shaft and supporting a hub and a stator aligned with themagnet, activation of said stator causing rotation of said shaft,rotation of said shaft relative to said hub being supported bylubricating fluid in first and second gaps defined between saidgenerally conical surfaces of said conical bearing members on saidshaft, complementary surfaces on said bearing seat and a centrifugalcapillary seal on one side of each said bearing and a grooved pumpingseal on the opposite side of each said bearing to isolate and containsaid fluid within said independent fluid dynamic bearings.
 12. Amagnetic disc storage system as claimed in claim 11 further including aseal cone supported from said shaft on an opposite side of said shaftfrom said central section and having a generally radial face cooperatingwith a generally radially extending surface of said conical bearingmember to define a further portion of said gaps of said fluid dynamicbearing.
 13. A magnetic disc storage system as claimed in claim 12further including grooves extending between a radially inner surface ofsaid conical bearing member and the surface of said shaft to define afurther portion of said gaps for said lubricating fluid, so that saidlubricating fluid may flow over and be maintained in contact withrelatively rotating surfaces of said conical bearing member, saidbearing seat, and said seal cone.
 14. A magnetic disc storage system asclaimed in claim 12 wherein the centrifugal capillary seal comprisesmeans for positively pushing fluid from an open end of a hydrodynamicbearing gap at each end of said shaft into said gap of each said fluiddynamic bearings.
 15. A magnetic disc storage system as claimed in claim12 wherein said capillary seal includes a surface of said seal coneextending at an acute angle away from said shaft and said bearing seatsupports a shield seal having a wall facing a wall of said seal cone todefine a reservoir between said walls, fluid between said wall beingforced into said fluid dynamic bearing with rotation of said conicalbearing member relative to said bearing seat, and a meniscus across saidfluid in said reservoir to prevent said fluid from escaping from saidcapillary seal and said fluid dynamic bearing.
 16. A magnetic discstorage system as claimed in claim 15 wherein said grooved pumping sealcomprises means for pumping fluid away from said central section of saidshaft towards said fluid dynamic bearing when said shaft is rotatingrelative to said bearing seats.
 17. A magnetic disc storage systemcomprising: a base, a rotatable magnetic storage disc having an axis ofrotation, a transducing head for reading and writing information on thedisc, a rotatable shaft supported in said base having a central sectionsupporting a magnet, and fluid dynamic bearings means fixed to saidshaft on opposite sides of said central section of said shaft locatednear to said base and distant from said base on the opposite side ofsaid magnet, for providing independent continuous lubricating gaps,bearing seats extending generally radially away from said shaft andsupporting a hub, and a stator aligned with said magnet, activation ofsaid stator causing rotation of said hub, rotation of said shaftrelative to said bearing seats being supported by lubricating fluid insaid independent continuous lubricating gaps defined by said bearingmeans.
 18. A magnetic disc storage system as claimed in claim 17including sealing means adjacent said fluid dynamic bearing means forestablishing sealing stiffness adjacent said fluid dynamic bearingmeans.
 19. Spindle motor supporting a shaft for rotation relative to ahub, the motor comprising separate fluid dynamic bearings mounted neareither end of the shaft, and on opposite sides of a magnet mounted on anexternal surface of a central section of the shaft intermediate to thefluid dynamic bearings, each of the bearings comprising a bearing conemounted on an external surface of the shaft and a bearing seat supportedadjacent the bearing cone, an inner surface of the bearing seatcooperating with an outer surface of the bearing cone to define a fluiddynamic bearing, and an outer surface of each of the bearing seatssupporting an end section of a hub.
 20. A spindle motor as claimed inclaim 19 wherein each of the bearing seats further supports a statorwhich is supported intermediate the outer surface of the bearing seatand an inner surface of the hub, the shaft supporting a magnet means forinteracting with the stator for establishing rotation of the shaft.